Known navigational aid systems have means for calculating trajectories between control points defined in a flight plan which may, for example, be provided by the pilot. The trajectories, calculated at the beginning of the flight and possibly updated during the flight, provide support for aircraft manoeuvres, whether they be decided by the pilot or by an automatic piloting system. In the known prior art, the calculated trajectory is split between a lateral trajectory, typically characterised by control points defined by a latitude and a longitude, and a vertical profile applied to this lateral trajectory to take account of the constraints, for example, of relief or fuel consumption management.
Among navigational aid systems, flight management systems (FMS) are known, a functional architecture of which is shown schematically in FIG. 1. In accordance with the ARINC 702 standard, they notably perform the functions of:
Navigation LOCNAV, 170, to perform the optimum localisation of the aircraft depending on geolocation means (GPS, GALILEO, VHF radio beacons, inertial navigation units, etc.),
Flight plan FPLN, 110, to input the geographical elements that make up the skeleton of the route to be followed (departure and arrival procedures, control points, etc.),
Navigational database NAVDB, 130, to construct geographical routes and procedures on the basis of data included in the databases (points, beacons, interception or altitude legs, etc.),
Performance database PERF DB, 150, containing the aerodynamic and engine parameters of the aircraft,
Lateral trajectory TRAJ, 120, to construct a continuous trajectory on the basis of the points of the flight plan, in accordance with aircraft performance and confining constraints,
Predictions PRED, 140, to construct an optimised vertical profile on the lateral trajectory,
Guidance GUID, 200, to guide the aircraft on its 3D trajectory in the lateral and vertical planes, while optimising speed,
Digital data link DATALINK, 180, to communicate with control centres and other aircraft.
On the basis of the flight plan FPLN defined by the pilot, a lateral trajectory is determined according to the geometry between the control points. On the basis of this lateral trajectory, a prediction function PRED defines an optimised vertical profile, taking account of any altitude, speed and time constraints. To do this, the FMS system has performance tables PERFDB which define the modelling of the aerodynamics and engines. The prediction function PRED implements the equations of the aircraft dynamics. These equations are based numerically on values contained in the performance tables to calculate drag, lift and thrust. The speed vector and the aircraft position vector are inferred therefrom through double integration.
Consideration of meteorological conditions and the changes therein adds to the complexity of the calculation of a flight trajectory. FIGS. 2a and 2b show a great circle trajectory 10 between a point A and a point B. The meteorological conditions in the surroundings of the trajectory are shown by means of a mesh MW; the direction and length of the arrows in each node of the mesh illustrating the direction and intensity of the wind vector W in this node. The wind vector is defined according to the 3 dimensions, and FIGS. 2a and 2b show the projection of the wind in the plane xy.
As the wind is not constant over the route, the great circle trajectory 10, the shortest trajectory to link A and B, does not turn out to be the most fuel-economical and/or the fastest. An overall optimisation calculation of the trajectory, such as, for example, dynamic programming, enables the construction of a trajectory 11 to link the points A and the point B in an optimised manner, in terms of fuel consumption and/or time. Such a calculation of an optimised trajectory depending on meteorological conditions requires substantial computing resources and a long calculation time. This calculation can be carried out in a computing station on the ground, but it is relatively unsuitable for use in an on-board flight management system.
Enhancement of the trajectory calculation of FMS on-board flight management systems has been envisaged by proposing means to divert an aircraft from its trajectory on the basis of wind information. The patent document published under reference FR2939505 is thus known from the applicant, said document describing an on-board solution for optimising the lateral trajectory, based on a local modification of the flight plan. The diversion is based on the DIRTO function known to the person skilled in the art and described in the ARINC 702 standard. The trajectory is modified in relation to the initial trajectory by adding a diversion point to replace a series of control points of the flight trajectory. The use of the DIRTO function necessarily restricts the complexity of the representation of the lateral trajectory to be followed. This implementation does not guarantee that an optimum trajectory in terms of fuel consumption and/or time will be obtained.
It therefore remains desirable to have effective navigational aid means for adapting a flight trajectory on-board the aircraft allowing further optimisation of fuel consumption and speed and constructing a trajectory in which the aircraft is, as far as possible, propelled by the wind.
One object of the present invention is to overcome the aforementioned disadvantages by proposing a navigational aid method allowing a new trajectory to be generated on the basis of a reference trajectory, allowing better use to be made of the wind, using fewer computing resources than in the prior art, compatible with an execution by on-board systems such as the FMS flight management system on-board the aircraft.